1. Field of the Invention
This invention relates to ethanol solutions of alkyl half-esters of maleic anhydride and a C.sub.1 -C.sub.4 alkyl vinyl ether, and, more particularly, to a process for making such solutions which are benzene and acetone-free.
2. Description of the Prior Art
Several processes are available for making ethanol solutions of alkyl, e.g. butyl half-esters of maleic anhydride and a C.sub.1 -C.sub.4 alkyl vinyl ether. For example, such solutions can be obtained from powders of maleic acid-C.sub.1 -C.sub.4 alkyl vinyl ether copolymers prepared by copolymerization of maleic anhydride and a C.sub.1 -C.sub.4 alkyl vinyl ether in benzene. In this process, such powders are half-esterified in excess butanol, followed by introduction of ethanol solvent and removal of remaining butanol. However, since this method requires the use of a considerable excess of butanol, some butanol may remain in the product. Furthermore, the half-ester must be heated to distill out excess butanol, and, under these conditions, a considerable amount of the corresponding ethyl half-ester copolymer is formed by transesterification of the half-butanol copolymer solution. In summary, the presence of undesirable benzene, butanol and ethyl half-ester in the solution product is objectionable from a commercial standpoint.
Another method known in the art avoids the use of benzene but introduces acetone as a solvent into the system. Residual acetone, free butanol and ethyl half-ester copolymer are found in the solution of this product. These solvents also are objectionable in commercial compositions, such as hair formulations. Furthermore the ethyl half-ester copolymer is less compatible with hydrocarbon propellants used in aerosol hair treatment products than the butyl half-ester copolymer.
For these and other reasons, it is desired to provide a new and improved process for making ethanol solutions of alkyl half-esters of copolymers of maleic anhydride and a C.sub.1 -C.sub.4 alkyl vinyl ether, which process overcomes the disadvantages of prior art methods of manufacturing such products.
Accordingly, it is an object of the present invention to provide a process for making ethanol solutions of alkyl, e.g. butyl half-esters of copolymers of maleic anhydride and a C.sub.1 -C.sub.4 alkyl vinyl ether in which residual amounts of solvents such as benzene and acetone are absent, and butanol solvent and ethyl half-ester copolymer by-product are minimized.
These and other objects and features of the invention will be made apparent from the following description of the invention.